The Cap Sizun is a headland forming the western extremity of the Cornouaille, in the French département of Finistère in Brittany, corresponding to the canton of Pont-Croix.
The best known sites in this region are the pointe du Raz, the pointe du Van, and, between these two points, the baie des Trépassés.
The Cap Sizun reaches out into the Atlantic Ocean, bordered to the north by the baie de Douarnenez, and to the south by the baie d'Audierne.
The territory of Cap Sizun is formed by the communes of Pont-Croix, Audierne, Plouhinec, Confort-Meilars, Mahalon, Esquibien, Beuzec-Cap-Sizun, Goulien, Cléden-Cap-Sizun, Primelin, Plogoff and the Île-de-Sein. This territory is covered by a commonality of communes (Communauté de communes du Cap-Sizun), which includes all the above communes except île de Sein.